Class 7 Geography Chapter 2 Important Notes

NCERT Class 7 Social Science

Class 7 Geography Chapter 2 Important Notes related to the chapter Inside our Earth

Earth has an onion-like structure with layers. Earth has several concentric layers. The Radius of the earth is 6400 kilometers.
 
Class 7 Geography Chapter 2 Important Notes
Image Source: https://www.nationalgeographic.org/

The Crust – Uppermost top layer

  • The thinnest layer of the earth.
  •  It includes Continental and ocean crust.
    • The thickness of continental crust: up to 35 km
      • Made of Silica and Alumina >> sial
    • The thickness of Ocean crust: up to 5 km.
      • Made of Silica and Magnesium >> sima
 
Class 7 Geography Chapter 2 Important Notes
Lithosphere

Mantle – Intermediate layer

  • It is the second layer of the Earth. It is about 2900 km below the crust.
  • The mantle can be divided into two layers, the upper mantle, and the lower mantle. 
  • The mantle is made of Silicate rocks that include 44.8% oxygen, 21.5% silicon, and 22.8% magnesium.
(Class 7 Geography Chapter 2 Important Notes)
 

Core – Innermost layer

  • Its radius (thickness) is about 3500 km.
  • Made of Nickel and Iron (ferrous). So it is called (ni + fe =) nife.
  • Pressure and temperature are very high at the core.
  • The core can be further dived into the inner core and outer core.
 
 
Class 7 Geography Chapter 2 Important Notes

Various landforms are found on the crust. These landforms are made of various minerals and rocks.

So rocks are the natural mass of minerals. Rocks have various sizes, colors, textures, properties, etc.

Major Types of Rocks

(Class 7 Geography Chapter 2 Important Notes)

  1. Igneous rocks (Derived from Ignis – Latin word for fire)
  2. Sedimentary rocks (Derived from Sedimentum – Latin word for settle down)
  3. Metamorphic rocks (Derived from Metamorphose – the Greek word for form)

Igneous Rocks

Igneous rocks are formed by cooling and solidification of molten magma (lava). They are also called primary rocks.
 
  • Intrusive igneous rocks (Plutonic rocks)

    – Formed by the cooling of the lava deep inside the earth’s surface.
    – Slow cooling.
    – Fine grains.
    – Example – Granite
    – Grinding Stones are made out of these rocks.

  • Extrusive igneous rocks (Volcanic rocks)
    – Formed by rapid cooling and solidification of magma out of the earth’s surface.
    – Rapid cooling.
    – Large grains.
    – Example – Basalt.
    – Deccan plateau is made of basalt rocks.

Sedimentary Rocks

(Class 7 Geography Chapter 2 Important Notes)

Igneous rocks break down into smaller pieces (sediments). These sediments are moved with water, wind, etc. these sediments get deposited at a place and compressed to form sedimentary rocks.

Fossils of animals, plants, etc are may be combined with the sediments and become part of sedimentary rocks.
Example – Sandstone, made of sand grains.

Metamorphic Rocks

(Class 7 Geography Chapter 2 Important Notes)

Change of Igneous or sedimentary rocks into metamorphic rocks under high pressure and temperature.
 
These metamorphic rocks change back to lava under high temperature and pressure.
 
Examples,
Clay changes into Slate
Limestone into Marble
 
 

Rock Cycle

One type of rock is changed into other types in a cyclic manner. Certain pressure and temperature conditions are responsible for these transformations. This process of transformation is called the rock cycle.
 
Igneous Rocks >> Sedimentary rocks

 

(Igneous rocks and sedimentary rocks) >> Metamorphic rocks

 

Metamorphic rocks >> Molten Magma >> Igneous rocks
 
Class 7 Geography Chapter 2 Important Notes
Image Source: Pinterest/Nasa.org

 

How Rocks are useful?

Used in constructions of monuments, buildings, houses, roads, etc.
  • Red fort is made of red sandstone.
  • Taj Mahal is made of White Marble.
 
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